I used to read a lot in class, and the teachers didn't care because they were focused on teaching students that needed more help. I had a calculator I played with, and found things like 1111^2 = 1234321, and tried to understand these patterns. I discovered the Collatz Conjecture this way, began to learn about exponential functions, etc.
I also learned to draw probability trees from an explanation of the Monty Hall problem I read once, and I think learning that at a young age helped Bayesianism feel intuitive later on, and it was a fun thing to learn.
Second the Anki recommendation, but I'm not sure it's the most fun thing.
Writing fiction was something I enjoyed too, and improved my communication skills.
Although my 8-year-old son likes his teacher, he is frequently bored at school. He attends a high quality suburban public school in the United States. He has a lot of traits in common with LessWrong readers, and we would like advice for what he can do to counter his boredom. Many of you must have found grade school more or less tedious. What were your coping strategies?